Seven years after the Sept. 11 attacks, U.S. intelligence officials believe they've won many small victories against al-Qaida's ability to finance its operations, but they remain unable to put a concrete dollar figure on their impact.

That's because they have no reliable estimate of al-Qaida's overall budget, according to current and former U.S. counterterrorism officials, which means the only measures of the organization's economic health are sporadic, anecdotal and fragmentary.

"When you see a cell complaining that it hasn't received its monthly or biannual stipend and it's unable to pay the salaries of the people in the cell, unable to make the support payments to the families of terrorists living or dead, that's a tremendous indicator we have pressured the financial channel," said Adam Szubin, the director of the U.S. Treasury's Office of Foreign Assets Control and the man in charge of tracking terrorist finance.

Intelligence agencies scan phone conversations, e-mails, fax transmissions and instant message traffic for hints they have thwarted the flow of money to al-Qaida and other jihadist groups. But they are unable to get a firmer grasp on the overall state of terrorist finances, in part, because of the nature of most operations.

"Terrorism is unfortunately not a rich man's sport," said a former OFAC official, meaning that it does not take a lot of money to carry out a major attack. Tracking those small numbers in the vast sea of global financial transactions is difficult.

Cost differentials
An NBC News analysis of attacks by al-Qaida and other Sunni extremist groups shows that only one cost as much as $500,000 — the Sept. 11, 2001, attacks on the United States. But others, like the 2005 attack on the London transit system or the 2000 attack on the USS Cole in Yemen, cost less than $15,000 to carry out.

At the bottom end of the scale, the simplest first-generation suicide bombs constructed by the Palestinian Islamist group Hamas, consisting of duffle bags filled with black powder from unexploded Israeli land mines and ignition switches from abandoned cars, cost no more than $200.

The money also is difficult to track because terrorists do not use the world financial system as extensively as they once did, due partly to U.S. success in cracking down on it.

"Part of it is that the U.S. is sitting on the international banking system," said Roger Cressey, deputy counter terrorism chief in the Clinton and Bush administrations and now an NBC News analyst.

The United States has sponsored a U.N. terrorism funding blacklist, which requires all member states to freeze the assets and impose an international travel ban on people and entities placed on the list.

No one wants to be placed on the U.N. list of 503 people and entities or OFAC's 404-page list of "Specially Designated Nationals," a voluminous compilation of everyone from Cuban tourist agents to Osama bin Laden. Officials said they have intelligence — gathered from electronic eavesdropping — of prospective donors expressing concern about giving money to a charity or other entity that's been listed.

"You'll hear them say 'I'm not giving money anymore to X, they've been listed'," said one official.

Lately, cracks have developed in the list, as legal challenges mount and political support drops, especially in Europe. But Szubin believes the splits are overblown and that European allies will succeed in maintaining the system.

Figure 'totally made up'
Despite the anecdotal successes Szubin cites, U.S. estimates of al-Qaida's budget are rife with problems, according to Richard Clarke, former boss of the White House counterterrorism office.

In 2003, the United States estimated that al-Qaida's budget before the Sept. 11 attacks was $35 million and that it fell to $5 million just two years after the attacks. Those numbers were repeated in the final report of the 9/11 Commission.

"That number was totally made up, totally made up," Clarke said of the $35 million figure.

Clarke explained the figure was based on limited real information. "I don't think there is an integrated budget. In U.S. business parlance, there are 'cost centers', but not an integrated budget," he said.

Even the most cited official measure, OFAC's annual tally of blocked al-Qaida assets, is by Szubin's own admission irrelevant to understanding the state of terrorist financing and the success of U.S. efforts.

OFAC's most recent report, issued in early October, lists $11.324 million in blocked al-Qaida assets, predominantly financial instruments. That number is up from $7.7 million the year before, mainly due to an increase in the number of people and organizations designated by Treasury as terrorists.

"Some have mistakenly drawn on figures of blocked assets as we summarized in our report," Szubin said. "There is a hunger for data and these are numbers, but we try to put a major caveat there and say we don't view these numbers as an indicator of the pressure we're putting on terrorist groups."

Clarke said the best indicator, beyond real-time intelligence gathering, is often the data found in laptops, documents, notebooks and calendars taken after a successful raid or arrest.

"When they do get a cell, you can grab financial documents and do an analysis, go back and find out how they moved their money and then move in on them," Clarke said.

That way, he said, you get a sense of what means they are using to move money and then can try to stanch the flow in the future. But because of al-Qaida's compartmentalization, it doesn't provide a good picture of the organization's financial health.

Turn to crime for funding
One thing analysts are sure about is that al-Qaida and other terrorism organizations are continuing to get money from somewhere, even if many of the international channels have been closed. Officials believe one of the biggest sources of money is simply "self funding," making money off legitimate businesses or crime.

"One pattern we've seen in southern Europe is counterfeiting, not of currency, but goods, travel documents, a skill you would expect a jihadi cell to have," Szubin said.

U.S. intelligence also has seen jihadis engaged in carjackings and theft. In North Africa, they are making a lot of money off the drug trade, not as primary suppliers or movers, but extorting suppliers or moves. "They will take a cut," Szubin said.

Some major drug dealers may have been helping as well.

Among those on the U.S. list is Dawood Ibrahim, an Indian underworld figure believed responsible for the 1993 terrorist attacks in Bombay that killed more than 250 people suspected of running one of south Asia's most effective heroin smuggling rings. Now, al-Qaida is using the same routes to smuggle cash, the Treasury said.

"Ibrahim's syndicate is involved in large-scale shipments of narcotics in the U.K. and Western Europe," according to a Treasury Department intelligence report.

"The syndicate's smuggling routes from South Asia, the Middle East and Africa are shared with bin Laden and his terrorist network. Successful routes established over recent years by Ibrahim's syndicate have been subsequently utilized by bin Laden. A financial arrangement was reportedly brokered to facilitate the latter's usage of these routes," the report stated.

Al-Qaida also has taken to using one of the most basic means of moving money: carrying it around in suitcases, briefcases and bags using trusted couriers.

While the United States claims to be making an effort to thwart cash couriers, Clarke said there is a cultural problem.

"In the Middle East, people do carry millions around in briefcases," he said. "It doesn't mean they're terrorists. It's just part of their culture, tradition."

'Fooling ourselves'
Michael Sheehan, former director of counterterrorism at the New York Police Department, believes that while there is a continuing need to push down hard on terrorism financiers, a lack of money is not going to deter attacks.

"You have to do it, you can't leave it unfettered, but it's never going to be determinative factor," said Sheehan, now an NBC analyst.

"Terrorists are always bitching about money. For two years before the 1998 embassy attacks, they bitched about money. Terrorists bitch about money the way soldiers bitch about the chow, but that doesn't mean the soldiers aren't going to fight or the terrorists aren't going to attack," Sheehan said.

More important and more difficult to shut down, according to Sheehan, is the funding by Saudi and other Gulf States of Islamic schools (the madrassas) and “charities” in Pakistan, “which may not be directly involved in terrorism but stir it all up.”

Former Congressman Tim Roemer (D-Ind.), a member of the 9/11 Commission and someone likely to have an intelligence role in the incoming Obama administration, agreed with Sheehan.

"We are only fooling ourselves if we think that financial action alone, or any other counterterrorism tool used in isolation, is sufficient to cripple al-Qaida," Roemer said.

"Terrorist groups sustain themselves not only through force of arms, but by rooting themselves in a variety of social and political factors in their host societies. Disrupting their cash flow is simply one tool among many other political, diplomatic and military tools that must be applied in combination to successfully destroy al-Qaida," Roemer said.

Robert Windrem is an NBC News Investigative Producer; Garrett Haake is an NBC News researcher.